Using liquid solutions (often referred to as liquid smoke) as a replacement for conventionally smoking foods by direct contact with wood smoke has become a standard industry practice. One known liquid smoke solution for flavoring and coloring foods is an aqueous liquid smoke flavoring described by Hollenbeck in U.S. Pat. No. 3,106,473. Another useful solution for flavoring and coloring foods is obtained from a process for isolating the organic components of the fast pyrolysis of wood or cellulose described by Underwood et al. in U.S. Pat. No. 4,876,108. When such liquid solutions are applied to the surface of meats and other protein-containing foods, organic components in the solution give a food a characteristic smoke flavor and react with the proteins of the food to give a brown, smoked color typical of a conventionally smoked food.
Surface appearance and flavor are important factors in the commercial and consumer acceptance of "liquid smoked" foods. A common feature of most varieties of such foods involves using various types of liquid solutions of wood-derived smoke constituents for imparting both characteristic flavor and color to the food.
The application of a liquid smoke solution to a food is generally carried out in a variety of ways including: spraying or dipping a food during processing, incorporating the liquid smoke in the recipe itself, or treating a casing which contacts a food during processing. The conventional operations of spraying or dipping a casing have not been completely satisfactory due to an inability to treat or coat the encased food uniformly. In addition, treating a casing with a liquid smoke solution does not always provide a food having the desired surface appearance. For example, when a liquid smoke solution is applied to a meat the processor normally must give up browning in order to keep the flavor at a desired level because the flavor imparting ability of known liquid smoke solutions is generally too intense at a desired brown color.
In addition, encased sausages treated by application of a conventional liquid smoke to a casing during processing have been found to yield (after peeling the casing from the sausage), sausages that are lacking in smoke color and that have poor color uniformity between sausages and batches of sausages. In addition to lack of uniformity of coloration when casings are treated with conventional liquid solutions, the surface of a treated sausage often may include light and dark streaks, light and dark blotches, uncolored spots or specks appearing at the ends of the sausage, dark surface discolorations or black spots appearing on the casing or on the sausage.
Furthermore, applying a liquid smoke to encased food products, such as by spraying or dipping, also causes unwanted pollution and equipment corrosion problems for the food processor.
It has also been reported that when a cellulosic casing, made from either fibrous or nonfibrous gel stock casing, is treated with a known highly acidic (pH of about 2.0 to 2.5), tar-containing, aqueous liquid smoke, tarry deposits accumulate on coating and squeeze rollers of conventional coating apparatus. These deposits cause the casing to stick to the rollers and eventually force a shutdown of the coating apparatus.
One reported method to minimize some of these problems associated with imparting smoke color and flavor to foods uses a "tar-depleted" liquid smoke solution to coat the surface of a casing. For example, unwanted tars may be partially removed from conventional liquid smoke by neutralizing the liquid smoke with base to precipitate the tars. Use of such a neutralized, tar-depleted liquid smoke to treat a casing helps to prevent the tarry deposit accumulation problem. Unfortunately, the neutralizing method for forming a tar-depleted liquid smoke is not satisfactory. Tar-depleted liquid smoke solutions have a strong flavor but do not have a sufficient coloring ability because the coloring ability of a liquid smoke solution is typically known to decline with increasing pH. Further, the viscosity of a liquid smoke solution increases substantially when the solution is neutralized especially after concentration. These factors limit most applications, particularly where a high coloring ability is desired.
Similarly, a solvent extraction process may be employed to make tar-depleted liquid smoke. Such a process is reported in U.S. Pat. Nos. 4,505,939, 4,431,032, 4,431,033, 4,496,595, 4,525,397, 4,504,501, 4,504,507, 4,657,765 and 4,717,576. In this process, a tar-containing liquid smoke solution is extracted with a nonreactive or reactive organic solvent which is immiscible in the liquid smoke solution under conditions sufficient to form a tar-enriched solvent fraction and a tar-depleted liquid smoke fraction. Using this solvent extraction method, it is possible to make a tar-depleted liquid smoke solution capable of imparting smoke color, odor, and flavor to foods.
The tar-depleted liquid smoke solution made from the solvent extraction process, unless it is neutralized, is generally still highly acidic, and thus may degrade or interfere with the integrity of cellulosic casings. If a tar-depleted liquid smoke solution is partially neutralized, the coloring ability also typically declines with increasing pH without a corresponding decline in flavor. Thus, satisfactory coloring with extracted liquid smoke solutions requires adding a solution having too much flavoring capability. Similarly, if enough of a tar-depleted liquid smoke solution is added to a casing to impart satisfactory color, the amount of organic components in the casing becomes to great. These overloaded casings may become rubber-like and cannot be handled or shirred. In addition, the process of adding large amounts of a tar. depleted liquid smoke solution to casings is very difficult using conventional techniques. Although tar-depleted liquid smoke solutions address some of the problems of using these solutions to color encased foods, the undesirable sensory aspects have been a factor for the lack of commercial acceptance of these products. There is a need in the industry for impregnated casings having both good coloring or browning properties and acceptable flavoring properties.